Process for stabilization of copper treated oils



Patented May 20, 1941 UNITED STATES PATENT OFFICE.

V 2,242,622 H or corrnu I Walter A. Schulze,

No Drawing. Original 2 Claims.

This invention relates to a new and useful process for treating hydrocarbon oil. More specifically, this invention relates to a process for stabilizing or preventing the deterioration of hydrocarbon oil which has undergone a purifying treatment with reagents containing copper.

This application is a division of our copending application Serial No. 239,731 filed Novemher 9, 1938.

Hydrocarbon oil, particularly petroleum distillates usually contain impurities, includingsulfur compounds, which cause the oil to exhibit undesirable properties such as bad odor and gum and color formation. It is customary, therefore, to subject said impure oil to a purifying treatment in order to remove the impurities or to convert them to less objectionable forms, for example, the conversion of mercaptans to disul- The methods of treatment for the removal or conversion of mercaptans make use of various chemical processes, and of these processes, one of the most satisfactory is the process utilizing copper, salts of copper, or solutions containing copper salts.

However, subsequent to treatment with coppercontaining reagents, it has been found that many hydrocarbon oils require further treatment or stabilization. This condition is due to the fact that said unstable oils retain from their contact with copper reagents, extremely small quantities of! oil-soluble copper compounds. These traces of copper compounds remaining in the oil are responsible for the marked acceleration of refrom said oil of small amounts of retained oilsoluble copper compounds responsible for aforesaid deterioration.

A further object of this invention is the production of hydrocarbon oil of good color and stable with respect to gum formation subsequent to treatment with copper-containing reagents.

A further object of this invention is the treatment of oil which retains traces of copper com- OILS Bartlesville, Okla, and Graham H. Short, Phillips, Ten, Petroleum Company, a corpo assignors to Phillips tion of Delaware application November 9,

Divided and this ap-- 337,734

reagents, to remove said copper from the oil, thereby delaying or preventing deterioration.

Another object of this invention is to provide a step in the sweetening of hydrocarbon oil with copper reagents whereby the sweetened oil is stabilized against deterioration by the removal therefrom of retained copper salts.

Another object of this invention is the conversion of oil-soluble copper compounds presentin hydrocarbon oil as a result of sweetening with copper reagents to oil-insoluble compounds, said conversion resulting in complete separation of I the insoluble copper compounds from the oil.

Schulze and Frey in U. 8. Patent No. 1,980,555

described a method for stabilizing an oil treated with copper.- and which exhibited discoloring and/or formation of resinous matter, polymers and oxidation. products; that is, a method of stabilizing the oil by bringing it in contact with an alkaline sulphide solution subsequent to treating with the copper reagent.

We have now discovered that copper treated oils may be stabilized by means other than the alkaline sulfide solution referred to above and that these means involve certain improvements and advantages. This discovery is extremely captide, the next number important in that it clearly defines the conditions which must be met to produce stabilized oils.

This discovery likewise makes it possible to divide I treating agents into two groups, the first group consisting of those reagents which will eflectively remove the hydrocarbon oil-soluble copper compounds and thereby stabilize the oil, and the second' group consisting of those reagents which will not remove sumcient quantities of the copper compounds to stabilize the oil.

We have found that copper mercaptides increase in solubility in the oil with increasing molecular weight of the mercaptans. Copper methyl mercap'tides is the most insoluble of all the copper mercaptides and is almost totally insolublein hydrocarbon oils. Copper ethyl merin the series, is a little more soluble, yet-its: actual solubility figure is extremely low. Copper butyl mercaptides and am] mercaptides are much more soluble and their solubilities may be determined in the usual manner of precise measurements.

We havenot discovered thathydrocarborr oil containing copper methyl mercaptide, and therefore completely saturated with respect to the substance, does not show any of the undesirable reactions mentioned above as resulting from the catalytic efiect of dissolved copper compounds.

pounds subsequent to sweetening with copper In other words. we have established that the con.--

centration of copper from a saturated solution of copper methyl mercaptide in hydrocarbon oil is too low to cause deterioration of the oils. On the other hand, we have found that if the hydro carbon is saturated with respect to copper ethyl mercaptide, the concentration of copper is just sufficient to cause a slow depreciation in' the said properties of the oil. Thus, we have established that there is a critical value for copper concentration in the oil, above which deterioration will occur, and below which the oil will be stable as regards gum and color formation in storage. This improved process of stabilization depends on the effective removal of traces of copper compounds from the contaminated hydrocarbon oil by treating said oil to completely convert the hydrocarbon oil-soluble copper compounds into compounds whose solubility is less than the solu-' bility of .the copper salt of ethyl mercaptan. By this means, and the subsequent separation of these more insoluble compounds from the hydrocarbon oil, the deterioration due to dissolved copper compounds in the oil is prevented.

Since the deterioration of oil is accelerated in a catalytic manner by dissolved copper salts, it follows that copper salts more insoluble than copper ethyl mercaptide are inactive as catalysts for deteriorative reactions in oil, and likewise possess marked resistance to oxidation processes which would change said insoluble copper compounds to more active forms which would be" injurious to the oil.

Oil-soluble copper compounds which may be soluble copper compounds into the less soluble copper methyl mercaptide. Complete removal of the copper is not effected by treatment of the oil with caustic soda, carbonate or phosphate solutions, or by the addition to the oil of controlled amounts of ethyl mercaptan.

In order to explain more exactly. the criterion by which the stabilization of copper-containing oil is judged, the relative solubilities of the copper compounds encountered may be considered.

The sulfides of copper are the most insoluble compounds of the metal. The mercaptides by reason of analogous structure exhibit similarsolubilities in water, but are slightly more soluble in oils due to the'organic nature of the alkyl or aryl group present in the mercaptide molecule.

The sulfides of copper have a solubility of about 0.00033 gram per liter of water and an infinitesimal solubility in hydrocarbon oils; the solubility of copper methyl mercaptide is approximately 0.000003 gram per liter of cracked naphtha, or about one-hundredth the solubility of copper sulfide in water. These solubility figures are based on extremely sensitive colorimetric tests, especially devised to indicate the presence and concentration of copper in hydrocarbon oil.

The following table shows the approximate solubilities of copper salts in oils, or the extent to which oil-soluble copper compounds are formed by contact of the oils with said copper salts for a 24 hour period.

Table I Dissolved cop- Oil-soluble copper Copper Salt IIy drocarbon 011 per compounds Parts per mil- Grams per 1,000 cc. on of oil 1 Copper oxide Doctor-sweet cracked naphtha. Greather than 0.0003 (approx.)

' 1. Copper carbonate (basic). do .do 0 0003(ripproxl Copper hydroxide ..do 0 0003 (approx Copper phosphate ..do 0 0003 (approx Copper cyanide (KCN i do 0.0003 (approx) Copper silicate..- (lu .0003 (approx.) Copper sulflte o. 0003 (approx) Copper-n-butyl-mercaptide..

Copper-t-butyl-mercaptide Copper-ethyl-mercaptide do 1 Spr. gr. or naphtha taken as 0.75.

formed in complex hydrocarbon oil mixtures, particularly in petroleum distillates, are usually mercaptides or salts of acidic components such as cresylic and naphthenic acids. Such compounds may be more soluble than copper ethyl mercaptide, and likewise may not be removed from an oil in which said compounds are dissolved unless the method of treating or stabilization forms therewith copper compounds less soluble than copper ethyl mercaptide. For example, after a. cracked naphtha has been in contact with copper oxide, copper carbonate or copper phosphate, sensitive tests show the presence of traces of copper remaining in the naphtha, whereas a portion of the same naphtha after prolonged contact with copper methyl mercaptide shows no evidence of dissolved copper compounds. Further, the small amounts of copper salts present in a cracked gasoline which has been sweetened with a cupric chloride solution may be removed by adding thereto a controlled amount of methyl mercaptan to convert the more It will be seen from the values listed in Table I that complete removal of copper from an .oil may not be accomplished by contacting said oil [with a reagent to form any of the copper salts listed. This fact is based on experimental data which proves that the deterioration of an oil due to dissolved copper is not prevented unless the copper content of said oil is reduced to a value less than 0.1 p. p. m. as shown in Table II.

Thus in order to prevent the deterioration of a hydrocarbon oil which has been treated with a copper-containing reagent, it is necessary to contained approximately methyl mercaptan. The results of this stabilization are illustrated below:

Orig Color Appearance Gasoline sample Copper test inal gig; gg i gg color storage Cracked gasoline-copper treated-unstabilized I Positive,greaterthan0.lp.p.m +24 16 Dark brown. Cracked gznoline-copper treated plus2per cent Negative, less than 0.1 p. p. m.... +24 +23 +22 color.

(vol.) of sour vapor recovery gasoline. v I

I This gasoline was doctor sweet.

EXAMPLE III treat said 011 in order to reduce the amount of dissolved copperto a value less than 0.1 p. p. m. This is accomplished according to our invention by converting the copper present in the oil into compounds withoila'solubility less than the oilsolub .ity of copper-ethyl mercaptide.

As examples of the practice of my invention,

the following examples are described:

' EXAMPLE I A sample of cracked gasoline which had been sweetened by treatment with a solution containing cupric chloride was separated from the copper reagent and divided into two parts. One part was stored without further treatment. To the was added solid copper ethyl mercaptide and shaken until the oil was saturated with the coppercompound and an excess remained. Portions of this gasoline were then treated with various reagents to vform copper salts less soluble than copper'ethyl mercaptide. Samples of each portion of gasoline stabilized with the various reagents ,were then stored for comparison with a stored sample of the original gasoline and with the original gasoline saturated with copperethyl ggrcaptide. The tabulation of results is given Table III 7 Color Color No. Gmline a p Copper test inal A color days days storage storage '1 Cracked gasoline-no additional treatment Negative 24 2 Ciiacged gasoline-saturated with solid copper-ethyl-mercap- Positive, approx. 124 if: 0.1 p. p. m. 3 i2v vamegle added 0.006 percent methyl mercaptan followed by Negative, less than +24 +22 +21 8 w 0.1 n1. 4 #2 sample-plus2per cont sour vapor recovery gasoline containd +24 +21 +20 5 a i iitttii i fi it m sampea y con ac e wi ine ueous sol tion of dithizone. u do +M +22 +21 6 #2 sample-contacted with ammoniacal solution of alpha-bendo +24 +22 +21 :0 crime. 7 #2 sample-contacted with aqueous solution of thionalid'c do 24 22 1 s #2 sample-contacted with aqueous solution of 5.7-dibromodo $24 $22 $21 9 rz i z h "m al 1 t a h samp e-con ac e W1 ammomac sou ion of let ldid thiocarbonate. y 0 +24 +22 +21 other portion was added a solution, of methyl mercaptan in sulfur-freehexane solution, the quantity added being suflicient to' cause the gasoline to have a methyl mercaptan content of 0.003 weight per cent. After the addition of the mercaptan, the gasoline was allowed to stand for These examples are illustrative of the manner in which deterioration is prevented in hydrocarbon oils containing soluble copper compounds, according to the practice of this invention and the critical value for allowable copper concentration in oil which is stable with regard to color This gasoline was doctor sweet; no trace oi mercaptan alter two days.

Exmnn II of the gasoline of sufllcient gasoline to amount to 2 perv alpha-benzoinoxime.

two'hours, after which it was washed with water and gum formation in storage is thus disclosed. and stored. The results of this stabilizing treat- 55 we claim: ment are shown below: 1. In the processor sweetening hydrocarbon E Appearance after 30 Gasoline samples Copper test 152! 7 days, days. storage storage Cracked gasoline unstabilized.- Positive, greater than 1 p. p. m.-.- +24 l6 Dark, brown gummy. Cracked gasoline plus 0.003 per cent Negative, less than 0.1 p. p. m..-. +24 +23 +22 color. methyl mercaptan oil with copper reagents. the step of stabilizing the sweetened oil to prevent deterioration due to retained oil soluble copper salts which comprises adding a small quantity of a stabilizing agent comprising alpha-benzoinoxime.

2.Theprocessasinclaima1inwhichthe stabilizing agent is an ammoniacal solution of wan-ran a. scnunzn. GRAHAM n. anon-r.

.01 weight per cent of. 

